VCR conrods for realizing a variable compression in internal combustion engines belong to the prior art. DE-A-10 2005 055 199 describes a VCR conrod, in which the effective conrod length is brought about by way of rotation of an eccentric which is mounted in the small connecting rod eye. Here, the eccentric rotation is firstly brought about by the forces which act on the gudgeon pin during the operation of the internal combustion engine and secondly hydraulic forces on a supporting mechanism.
Said supporting mechanism limits the rotating speed of the eccentric and prevents undesired rotating back of the eccentric. The supporting mechanism which is known from DE-A-10 2005 055 199 consists of a pair of slider crank mechanisms on both sides of the eccentric, the pistons of which are supported in each case on fluid-filled supporting chambers. By way of a corresponding hydraulic connection of said supporting chambers, the desired reverse rotation lock and the desired braking action are realized.
One disadvantage of said VCR conrod is the increase in the (oscillating) mass in comparison with a conventional conrod. Moreover, the supporting mechanism, in particular the lever which is connected to the eccentric, requires a corresponding clearance in the interior space of the piston.
An adjustment toward high compression requires upwardly directed forces on the gudgeon pin, as occur during the phase of the gas exchange. That part of said gudgeon pin force which is caused by the centrifugal force increases as the square of the rotational speed. Conversely, the result of this is that the force which is available is reduced by the square of the rotational speed. As a consequence, the adjusting time increases greatly at low rotational speeds, as a result of which the thermodynamic potential of the variable compression can be used only incompletely in transient operation.
Moreover, DE-A-10 2005 055 199 discloses a reciprocating piston internal combustion engine having an adjustable variable compression ratio in a reciprocating piston by means of an actuating unit. The actuating unit is actuated by way of an adjusting mechanism, the adjusting mechanism having a rack and pinion drive. Here, the actuating unit and the adjusting mechanism are arranged outside a conrod of the reciprocating piston internal combustion engine. An arrangement of this type is very expensive and therefore requires a large amount of installation space in the internal region of the piston.
Furthermore, EP-B-1 496 219 describes an internal combustion engine with a variable compression ratio and DE-A-10 2012 014 917 describes a pressure pulse actuation means for a device for adjusting a variable compression ratio.